The swift waters of the East Fork Black River flow through a canyonlike
gorge called a "shut-in" at Johnson's Shut-Ins
State Park. These igneous rocks were formed nearly 1.5 billion
years ago when violent volcanic eruptions threw ash and
hot gases into the air. As these materials settled to the ground
and cooled, they formed the rhyolite rock seen at the park today. In
low places, the swift Black River became shut-in by the hard igneous
rocks, swirling and churning to form huge potholes, and breaking
away the weaker rock to create natural water slides and canyon-like
gorges.

This immense natural playground is the primary feature of the 180-acre Johnson’s
Shut-Ins Natural Area, only a portion of the 8,549-acre Johnson’s Shut-Ins State
Park. The history and geology of Johnson's Shut-ins is truly fascinating. Read
in-depth information and see more photos of Johnson's Shut-ins at www.missouristateparks.net. Learn
about the recovery of Johnson's Shut-ins after the breach of the Taum Sauk Reservoir,
the "new" areas and the extensive restoration of the park where
900 million years of Earth’s history
was revealed in the scour area of the breach (a "silver-lining" to geologists
worldwide).